Electronic amplifier and modifier



Aug.27, 1946. R; ROWE 42,406,565

ELEC'IRON IC AMPLIFIER AND MODIFIER Filed Oct. 15, 1943' By w I IIAVTIIORN'EK' i Patented Aug. 27, 1946 UNITED STATE PATENT OFFICE Myinvention relates, generally, to an electronic amplifier and modifierfor controlling and modifying the effective grid voltage-anode currentcharacteristics in electron tube circuits and, more specifically, to animproved circuit for sensitive control devices. l

The designof amplifying, modulating, signalling, counting, cycling andlike apparatus which depends for its function on variations inelectronic tube anode-cathode voltage and current i well known in theelectronic art.

In vacuum tube amplification; variations in anode current through aserially connected resistor develop a varying potential for applicationto the grid of th ensuing tube. In modulation, variations in the radiofrequency amplifier plate voltage produce similar variations in thecarrier power output. In photoelectric, inductive, capacitive and likeapparatus, variations in associated vacuum tube anode currents operateserially coupled resistors, relays and other current responsi'vedevices. 1

In all of these and many other systems it is the variation in current orthe variation in voltage, the maximum to minimum ratio, which in a largepart determines the effectiveness of the control. In conventionalamplifiers the variation in voltage or the voltage swing on the grid ofthe tube is a determining factor in the output volt age of the stage. Inconventional modulators the variation in anode-cathode radio frequencyamplifier voltage largely determines the percentage modulation. Inphotoelectric, inductive and capacitive apparatus the amount ofvariation in anode current largely determines the reliability, ruggednesand efficiency ofthe entire device.

I have found, however, that for many applications the variation involtage or current, the maximum to minimum ratio, is insufficient toproperly actuate the coupled device. Particularly in photoelectric,inductive and capacitive equipment fragile, expensive, sensitive relaysmust be used to respond to the small current changes produced. Further,these ensitive'relays usually are not designed to handl high secondaryvoltages and currents. Often, they are used in the control circuits oflarger relays with high secondary power handling capabilities adding tothe expense and complexity of the apparatus'.. Still further, sensitiverelays are more susceptible to damage and faulty operation due to lowcontact pressure and other effects.

It is, accordingly, anobject of myinventionto;

amplify these variations in current and voltage to increase the maximumto minimum ratio.

8 Claims. (Cl. 25027) Still another object of my invention is to furthercontrol or modify these variations, the ratio, rate and slope of maximumto minimum, to effect new and'useful circuit characteristics.

The aforementioned objects and other objects ancillary thereto I preferto accomplish, in short, by inserting serially in the master circuit acontrollable resistance devic with at least an anOde', control grid andcathode together with a means for biasing the control grid of theresistive element which is responsive to current or voltage variation inthe master circuit.

' Other and further objects of my invention reside in the method andapparatus employed therein as set forth more fully in the specificationhereinafter following by reference to theaccompanying drawing, in whichThe single figure schematically illustrates a capacity sensitive circuitarrangement embodying one of the principles of my invention.

With reference to the drawing, in which oathode heaters are eliminatedfor convenience in drawing, master tube l is employed in a modifiedHartley oscillator circuit, with variable condenser. 2 and inductance 3comprising the resonant tank' circuit. Plate blocking condenser 4 offersa low impedance to radio frequency current, but effectively isolate thedirect current component on plate 5 of vacuum tube I from the groundedtank coil assembly. Radio frequency choke 6 offers a low resistance tothe flow of direct current but a high impedance to the alternatingcurrent component appearing on plate 5 of vacuum tube l. By-passcondenser l effectively shunts to ground stray radio frequency currentswhich are not'im-' peded by choke fi. Grid condenser 8 offer a lowimpedance to regenerative radio frequency current inductively obtainedfrom tank coil 3 to provide excitation for grid 9 of tube I, buteffectively isolates grid 9 from ground. I have found that shunting gridcondenser 8 by a resistor as usually employed in the Hartley circuitpartially impairs sensitivity of this particular-arrangement and that,especially when condenser 8 exhibits appreciable leakage conductance,additional resistance may bev omitted. The resistance from grid 9 to thecathode of tube I is somewhat critical in securing optimum circuitsensitivity and the a shown in the drawing to leads A and B, is ineffect a variable resistance device across leads A and B, the resistanceof which varies in accordance with th condition of resonance or anti- 3alower than maximum value. voltage on grid26 of tube 24 decreases asdetermined by the IR drop acros resistor 25. Because Zof the lowernegative bias on grid 26 of tube 24, anode 23 begins to draw morecurrent through resistor 22 and more negative bias appears on grid 20 oftube I8. With increasing negative grid resonance in the link-coupledexternal tank circuit described below.

Pickup coils II) and I! provide link coupling to the capacity-sensitiveexternal tank circuit com prising coil I2, condenser I3, antenna I4 andground.

Normally closed relay I5 controls the signal-. ling, counting, cyclingor like circuit to be operated by capacity variations in the externaltank circuit. When the generator circuit comprising tube I and itsassociated components is oscillating, by proper selection of componentsthe external tank circuit comprising coil I2, condenser' The resistanceof tube I8 progressively increases I3, antenna I4 and ground can betuned to resonance with the oscillator. Components can be so adjustedthat when the external tank circuit istuned to resonance with.the'oscillator, tube I will draw maximum anode current, and when thiscondition of resonance is disturbed by addedcapacity between antenna I4and ground tube I will draw less than maximum anode current.

Thus,'in a condition of resonance, current responsive relay I5 will holdopen contacts I6 and I1 which control the external signalling,,counting,cycling or like circuit. Whenresonance is disturbed by a capacitancevariation in the link coupled external tank circuit, the armature ofcurrent responsive relay I5fwill drop out and close contacts I6 and I1.known in the electronic art.

'However, I have found that the anode current 1 change through currentresponsive relay I5 from g a condition of resonance to ofi-I'esormnce asoc-. casioned by the capacity changes :which I'en-. counter isinsufiicient to properly operate, the

relay which I desire to employ.

One phase of my invention resides in the hereinafter' describedimprovements; wherein a resistive device, vacuum tube I 8, comprising atleast an anode I9, control grid andcathode ZI is inserted serially inthe mastercircuit, that is to say, in series, with battery C, relay I5,resistor and. oscillator supply leads A and B; and

This circuit is well wherein. bias potential on control grid 20 issupplied by theIR drop through resistor 22 as deup termined-by the anodecurrent of anode 23 of I vacuum tube 24; and wherein the anode currentof vacuum tube. 24 is responsive to current changes 3 in ,the mastercircuit through resistor 25, grid j 26 and cathode 21.

V In a condition of resonance between the oscil-, j

22 and minimum bias appears on the grid 20 of tube I8 islow, a maximumvoltage appears on In a condition of oiT-resonance between theoscillator and the link. coupled external circuit as occasioned bythecapacitive changes which I encounter, the anode current of tube drops toThus, the bias lator and the link coupled external circuit the I I anodecurrent of tube I is maximum. Thus, the bia voltage on grid 26 of tube24 is maximum" 1 as determined by the IR drop acrossresistor 25 Becauseof high negative bias on grid 26 of tube 24, anode 23' draws littlecurrent through resistor tube I8. ;With low grid bias, the resistance ofat each end. When weak signals and lowgrid spacing. As the. grid bias ismade more negative I r to handle larger input signals, the electron flow1 'of the grid voltage-anode current curve, the

plification factor or mu of the tube remains sub- 'and current flowingin the master circuit through the field coil of relay I5 progressivelydecreases to an equalization point.

controlrelay. I am able to employ less expensive, more reliable currentresponsive relays, .se-

cure greater sensitivity of the capacitive element and insuresh'arperand more reliable relay action. Obviously, relay I5 may beinserted serially between the cathode oi? tube I and resistor 25, aboveor below-the junction of cathode Z'I; or between radio frequency choke tand cathode 2I of tube I8, to further increase sensitivity byeliminating the reactive plate current component of tube 24.

Otherwise, my invention has broad application in the radio andelectronic art. In the case of conventional electronic tube amplifiers,the IR voltage drop developed across a resistor inserted serially in theanode-cathode circuit is impressed on the grid of the ensuing tube. Whenthese tubes are operated on the straight-line portion stantiallyconstant and the maximum to minimum voltage or current ratio throughoutthe system remains substantially uniform- Although the peak values ofcurrent or voltage are elevated, the minimum values are similarlyelevated, in a manner such that the ratio between the two remainsconstant. By inserting my'controlled resistive element serially in oneor more of the amplifier stages, I have found that I can either increaseor decrease the ratio between the maximum and minimum values of currentor voltage by slight circuit modifications. Thus, it

becomes feasible to augment the amplification V factor of an amplifyingstage, or modify it in a desirable manner. It is to be understood that Ido not pretend to modify the inherent characteristics of a given vacuumtube, but only the effective characteristics of th circuit entity.

To reduce cross-modulation and modulationdistortion in radio receiversand to obtainother known effects, manufacturers are supplying so-'called super-control or remote cut-off amplifier tubes of a modifiedgrid structure designed to handle both large and small grid inputsignals with a minimum of distortion over a wide range. As noted on page15 of the R. C. A. Receiving Tube Manual, Technical series, PUG-14, thegrid of the super-control amplifier is wound with coarse spacing in thecenter and close spacing bias are applied to the tube, the effect 'ofthe nonuniform turn spacing of the grid on tube characteristics inessentially the same as for uniform from the sections of the cathodeenclosed bythe "ends of the grid is out on. The tube characterv isticsare then"? dependent on the: electron flow through the coarsetsection'of the grid. As noted furthenwh'ile the curves manifest by'the super;control grid and the uniformly 'spacedgrid are similar at small gridbias and high plate current ratings, the plate current of thesuper-control amplifier drops mor -slowly with large valueslof biasvoltage. i I i I have found that-'I am able to secure thisaforementioned super-control, remote cut-off and variable mu functionusing a tube with a uniformly spaced grid structure if I employ theprinciples of my invention and insert a variable resistance elementserially in th master circuit and control its resistance from currentflow in the master circuit.

To amplitude modulate a radio frequency am.- plifier, the amplifiervoltage is increased and reduced by the conventional modulators atmodulation frequencies. ing serially, in place of the secondary of amodulation transformer for example, the variable resistance elementherein disclosed I am able to accomplish the same effect when I controlthe resistance of the resistive device at modulation frequencies.Further, by the incorporation of a current responsive control means suchas I have illustrated in Figure 1, as tube 24 and its associatedcomponents, and by designing this means to keep the proper average platevoltage on the radio frequency amplifier, I can increase the sensitivityof this modulation means to the point Where it is practical.

While I have described my invention in only several of its preferredembodiments I am aware that various alterations and modifications of thepresent invention may become apparent and immediately suggest themselvesto those versed in the art to which. this invention is directed. Thus,any and all such alterations and modifications are to be consideredwithin the purview of the present invention except as limited by thehereinafter appended claims.

What I claim is:

l. A circuit arrangement for amplifying the current change in a seriescircuit, comprising in series a source of at least substantiallyconstant voltage, a variable resistance control device, a currentresponsive device constituting a load, and the anode and cathode of anelectron tube, further provided with at least one control gridelectrode; resistance means connecting the grid and cathode of the lastnamed electron tube, means to supply a potential difference between thelast named electrodes, said means consisting of a second electron tubewith at least an anode, cathode and control grid electrode, and meansfor connecting the anode of the second named tube to the grid of thefirst named tube and the grid and cathode of the second named tubeacross a resistance placed in the series circuit, whereby the maximum tominimum current ratio in the series circuit .is increased.

2. A circuit arrangement for amplifying the current change in a seriescircuit, comprising in series a source of at least substantiallyconstant voltage, an electron tube oscillator constituting with itsoutput circuit a variable resistance control device, a currentresponsive device constituting a load, and the anode and cathode of anelectron tube, further provided with at least one control gridelectrode; resistance means connec ing the grid and cathode of the lastnamed electron tube, means to supply a potential difference between thelast named electrodes, said means I have found that by insertl 6consisting-eta second electron tubeiwith at least an anode, cath'odeandcontrolgrid electrode,

andmeans' for'connecting the anode of the sec-' 7 on'd named tube 'tothe grid of the first named tube and the grid and cathode of the secondnamed tube across a resistance placedin the series circuit; whereby themaximum to minimum current ratio in the series circuit is increased.

3. A circuit arrangement for amplifying the currentchange in aseriescircuit, comprising in series'a sourceof at least substantiallyconstant voltage, a variable resistance control device, a relay deviceconstituting a load, and the anode and cathode of an electron tube,further provided with at least one control grid electrode; resistancemeans connecting the grid and cathode of the last named electron tube,means to supply a potential difference between the last namedelectrodes, said means consisting of a, sec-- ond electron tube with atleast an anode, cathode and control grid electrode, and means forconnecting the anode of the second named tube to the grid of the firstnamed tube and the grid and cathode of the second named tube across aresistance placed in the series circuit, whereby the maximum to minimumcurrent ratio in the series circuit is increased.

4. A circuit arrangement for amplifying the current change in a seriescircuit, comprising in series a source of at least substantiallyconstant voltage, an electron tube oscillator constituting with itsoutput circuit a variable resistance control device, a currentresponsive device constituting a load, and the anode and cathode of anelectron tube, further provided with at least one control gridelectrode; resistance means connect ng the grid and cathode of the lastnamed electron tube, means to supply a potential difference between thelast named electrodes. said means con-,

sisting of a second electron tube with at least an anode, cathode andcontrol grid electrode and means for connecting the anode of the secondnamed tube to the grid of the first named tube and the grid and cathodeof the second named tube across said load.

5. A circuit arrangement for amplifying the current changein a seriescircuit, comprising in series a source of at least substantiallyconstant voltage, an electron tube oscillator constituting with itsoutput circuit a variable resistance control device, a relay deviceconstituting a load, and the anode and cathode of .an electron tube,

further provided with'at least one control grid electrode; resistancemeans connecting the grid and cathode of the last named electron tube,means to supply a potential differencebetween the last named electrodes,said means consisting of a second electron tube with at least an anode,cathode and control grid electrode and means for connecting the anode.of the second named tube to the grid of the first named tube and theseries a source of at least substantially constant voltage, a relaydevice, 'a negative impedance, and. a variable impedance control device;said last named impedance including the anode cathode circuit of anelectron tube oscillator provided with a loadcircuit adaptable toresonance or anti-resonance with said oscillator, whereby the anodecircuit impedance of said oscillator is con" trolled by the tuning ofsaid load-circuit.

ROBERT G. ROWE.

